The subscriber end of a Fiber-To-The-Home (FTTH) or Fiber-To-The-Premises (FTTP) network terminates a fiber optic cable in an optical network terminal (ONT) positioned at an interior or exterior location on a subscriber's premise. As a result, a substantial amount of bandwidth can be made available to the subscriber to provide a variety of services, such as plain old telephone service (POTS), Internet access service, and television service.
One of the requirements of a POTS provider is to insure that telephone service is available for a period of time, such as eight hours, after a power failure. In an FTTH network, this is accomplished by providing a battery backup at the subscriber's premise. Thus, when power is lost, the battery backup at the subscriber's premise provides power to the ONT at the subscriber's premise to maintain the telephone service for the required period of time.
Although current-generation batteries perform for extended periods of time, even the best batteries will need to be replaced a number of times during the expected lifetime of an ONT. To insure uninterrupted service, the batteries are continuously monitored. As a result, when the performance of a battery falls below a predefined limit, the condition is detected and reported to the central office.
FIG. 1 is a block diagram that illustrates the subscriber end of an FTTH network. As shown in FIG. 1, the FTTH network includes a power injector 102, a power splitter 104, an ONT 106, and data terminal equipment (DTE) 108. The power injector 102 is located in the subscriber living area and the power splitter 104 and the ONT 106 are typically remotely collocated on the outside wall, garage, or basement. Two cables are used to connect the power injector 102 to the remotely located power splitter 104 and ONT 106. A category-5 (Cat5) cable connects the power injector 102 to the power splitter 104 for data and power, and a separate five-conductor cable connects the power injector 102 to the ONT 106 for battery status information.
Twisted-pair cables are commonly installed in residential settings to provide data service, such as Internet service. Newer homes utilize twisted-pair cable (e.g., Cat3/Cat5/Cat5e/Cat6) that usually has four pairs of wires, or four twisted pairs. In many cases, however, particularly in older homes, the twisted-pair cable has only two pairs of wires, one to transmit the data and the other to receive the data. Power is remotely delivered to the power splitter 104 over the same pair of wires as specified in the Power-over-Ethernet (PoE), IEEE802.3af standard. For this discussion two-pairs of wires are assumed, but it is understood that the concepts described herein may be applied to any number of wires. Data is transparently passed between the ONT 106 and the DTE 108 over the same twisted pairs. In an alternative embodiment, other types of cables, such as coaxial cable, may be used instead of Ethernet cable.
As shown in FIG. 2, the power injector 102 includes a power supply 202 that is connected to a power sourcing device (PSE) 204 at input node N1. The power supply 202, which plugs into a standard AC wall outlet, converts 115 VAC into a DC voltage, such as 54V.
In addition, the power injector 102 includes a battery module 206 that is also connected to the power sourcing device 204 to place a lower DC battery voltage, such as 48V, in the event that power supply 202 can no longer provide the necessary voltage. The power supply 202 and the battery module 206 are commonly referred to as an uninterruptable power supply (UPS).
The voltage at the input node N1 of the power sourcing device 204 is injected on the two pairs of Ethernet cable at an output node N2 of the power sourcing device 204. The power sourcing device 204 manages the power delivery to remotely powered devices as per IEEE 802.3af. The positive supply is placed on one pair and negative supply is placed on the other pair of the cable via center taps of data interfacing transformers 208.
The battery module 206 includes a rechargeable battery 210 that, when fully charged, outputs the lower DC battery voltage (12V). The rechargeable battery 210 can be implemented with any number of commercially available rechargeable batteries, such as lead acid, lithium ion, and other similar types of batteries.
The battery module 206 also includes a charge control circuit 212 that is connected to the rechargeable battery 210. When the power supply 202 fails, the charge control circuit 212 passes the DC voltage from the rechargeable battery 210, via a DC-to-DC converter within the charge control circuit 212, to the input node N1 of the power sourcing device 204. On the other hand, when the power supply 202 is functioning, the charge control circuit 212 can recharge the battery by passing a current from the power supply 202 to the rechargeable battery 210.
In addition, the battery module 206 includes a voltage sensor 214 that is connected to the input node N1 of the power sourcing device 204 to sense the magnitude of the voltage. Further, the battery module 206 includes a controller 216 that is connected to the charge control circuit 212 and the voltage sensor 214. The controller 216 can be implemented with a microprocessor or as logic implemented in, for example, a gate array or an application specific integrated circuit (ASIC). The charge control circuit 212, the voltage sensor 214, and the controller 216 each receive operating power from the rechargeable battery 210 which, as noted above, is charged by the power supply 202.
In operation, the voltage sensor 214 detects the voltage on the input node N1 of the power sourcing device 204 and transmits a value that represents the sensed voltage to the controller 216. During normal operation, the voltage sensor 214 detects the voltage output by the power supply 202 (e.g., 54V) and transmits a corresponding value to the controller 216. In this case, the controller 216 commands the charge control circuit 212 to recharge battery if needed.
On the other hand, when the voltage from power supply is no longer available, the voltage sensor 214 detects the falling voltage and transmits a value that represents the voltage to the controller 216. When the falling voltage reaches a predetermined level, such as 47V, the controller 216 commands the charge control circuit 212 to place the voltage from the rechargeable battery 210 on the input node N1 of the power sourcing device 204.
In addition to controlling the charging and use of the rechargeable battery 210, the controller 216 also reports the status of the rechargeable battery 210. The controller 216 can report, for example, whether the power supply 202 or the rechargeable battery 210 is providing a voltage to input node N1 of the power sourcing device 204, and whether or not the rechargeable battery 210 is charged or needs charging. Further, the controller 216 can determine and report whether the rechargeable battery 210 needs replacing by measuring how long it takes for the rechargeable battery 210 to become charged, as well as other factors that indicate the state of the rechargeable battery 210.
As further shown in FIG. 2, the power injector 102 also includes a battery status cable 218 that is connected to the controller 216 of the battery module 206. The battery status cable 218 has a number of wires, such as five, that provides battery status information from the controller 216 to the ONT 106. The power (either from the rechargeable battery 210 or the power supply 202) is injected in a data cable 220 (e.g., an Ethernet cable), which is connected to the power splitter 104. Both the power injector 102 and the power splitter 104 pass data signals transparently between the ONT 106 and the data terminating equipment 108. (An integrated access device (IAD) or a residential gateway (RG) can be used in lieu of the ONT 106.)
FIG. 3 illustrates the power splitter 104 in greater detail. As shown, the power splitter 104 splits the power from the data cable 220 via the center taps of transformers 310 and delivers regulated 12V to the ONT 106. The power splitter 104 includes a powered-device (PD) chip 302 that connects to an input node N3 via a diode bridge 304. The input node N3 is connected to the same power carrying wire pairs in the data cable 220. The diode bridge 304 ensures that the PD chip 302 is polarity protected. The PD chip 302 provides in-rush current limiting, over voltage protection, and DC signatures to allow adequate power delivery from the remote end as per IEEE 802.3af. After proper authentication, the PD chip 302 passes the power (voltage) to a DC-to-DC converter 306, which supplies the isolated voltage 12V to an output node N4. The isolated voltage 12V at the output node N4 is coupled to the input node N5 of the ONT 106 via a power cable 308. The power splitter 104 transparently passes the data on the same pairs of cable to the ONT 106 at an output node N6. The power splitter 104 can also optionally be integrated into the ONT module 106.
FIG. 4 illustrates a detailed view of the ONT 106. As shown, the ONT 106 includes a voltage sensor 402 and last-gasp circuit 404, both of which are connected to the input node N5, which is connected to the node N4 in the power splitter 104 via the power cable 308 (see FIG. 3). The input node N5 also powers the rest of the ONT 106.
Further, ONT 106 includes a controller 406 that is connected to the battery status cable 218, the voltage sensor 402, and the last-gasp circuit 404. As discussed above, the voltage sensor 402, the last-gasp circuit 404, and the controller 406 each receives operating power from the power supply 202 or the rechargeable battery 210, depending on which source is functioning.
When the power supply 202 and the rechargeable battery 210 (see FIG. 2) both fail to provide the voltage needed by the ONT 106, the voltage sensor 402 detects and reports this condition to the last-gasp circuit 404. The last-gasp circuit 404, in turn, outputs a voltage to the ONT circuit for a period of time that allows the controller 406 to gracefully shut down. The last-gasp circuit 404 can utilize, for example, a capacitor (not shown) to store a finite amount of energy to be delivered to the ONT circuitry. The ONT 106 can be implemented without last gasp circuit.
To prevent a total loss of power, the status of the rechargeable battery 210 (see FIG. 2) is continuously monitored. As noted above, the controller 216 of the power injector 102 can output status signals that indicate, for example, whether the power supply 202 or the rechargeable battery 210 is providing a voltage to the second pair of wires, whether or not the rechargeable battery 210 is charged or needs charging, and whether or not the rechargeable battery 210 needs replacing.
Referring back to FIG. 4, the controller 406 of the ONT 106 receives the battery status signals from the controller 216 in the power injector 102 and passes the status information along to the central office (not shown) as necessary. As a result, when the rechargeable battery 210 (see FIG. 2) begins to fail and needs replacing, the condition can be detected and the responsible party notified before total battery failure results.
As can be appreciated, the type of system described above requires two cables to be installed from the power injector 102 and the ONT 106, which is remotely located from the power injector 102. Installing the separate battery status cable, however, can become quite expensive and/or inconvenient in a subscriber setting. Thus, there is a need for a system and method of easily delivering battery status information from the power injector to the ONT.